Data from: Experimental evolution of bet hedging under manipulated environmental uncertainty in Neurospora crassa

All organisms are faced with environmental uncertainty. Bet-hedging theory expects unpredictable selection to result in the evolution of traits that maximize the geometric-mean fitness even though such traits appear to be detrimental over the shorter term. Despite the centrality of fitness measures to evolutionary analysis, no direct test of the geometric-mean fitness principle exists. Here, we directly distinguish between predictions of competing fitness maximization principles by testing Cohen's 1966 classic bet-hedging model using the fungus Neurospora crassa. The simple prediction is that propagule dormancy will evolve in proportion to the frequency of ‘bad’ years, whereas the prediction of the alternative arithmetic-mean principle is the evolution of zero dormancy as long as the expectation of a bad year is less than 0.5. Ascospore dormancy fraction in N. crassa was allowed to evolve under five experimental selection regimes that differed in the frequency of unpredictable ‘bad years’. Results were consistent with bet-hedging theory: final dormancy fraction in 12 genetic lineages across 88 independently evolving samples was proportional to the frequency of bad years, and evolved both upwards and downwards as predicted from a range of starting dormancy fractions. These findings suggest that selection results in adaptation to variable rather than to expected environments.

所有生物均面临环境不确定性。风险对冲理论（bet-hedging theory）认为，不可预测的选择压力会推动性状演化，使几何平均适合度（geometric-mean fitness）达到最大化——尽管此类性状在短期内看似有害。尽管适合度测度是进化分析的核心议题，但目前尚无针对几何平均适合度原则的直接检验。
本研究以粗糙脉孢菌（Neurospora crassa）为实验材料，检验Cohen于1966年提出的经典风险对冲模型，以此直接区分不同竞争型适合度最大化原则的预测结果。该理论的简单预测为：繁殖体的休眠程度将随“灾年”发生频率成比例演化；而算术平均适合度（arithmetic-mean fitness）原则的预测则是，只要灾年发生概率小于0.5，就会演化出零休眠的性状。
我们设置了5种不同不可预测“灾年”发生频率的实验选择处理组，使粗糙脉孢菌的子囊孢子（ascospore）休眠比例发生演化。
实验结果与风险对冲理论一致：在88个独立演化样本的12个遗传谱系中，最终休眠比例与灾年发生频率呈正相关，且无论初始休眠比例高低，休眠比例均会按照预测方向向上或向下演化。
本研究结果表明，自然选择驱动的适应性演化是针对可变环境，而非单一预期环境的。